In the art of paper manufacturing, decontamination of the paper pulp is of primary importance to achieve a consistent paper product. In particular, recycling waste paper requires extensive cleansing of the aqueous paper pulp to remove extraneous contaminates. Waste paper materials present a challenge to provide an economically feasible means of recycling which yields an acceptable paper product.
Contaminates may be grouped into one of three classes. First, elongated flexible materials, such as pieces cord, fabrics and wire can be removed from the pulp relatively efficiently by a ragger, well-known in the art. A ragger is generally a rope trailing in the pulper vat upon which elongated material becomes entwined. Second, heavy materials, such as rocks and metal pieces, are typically removed with increased effort by screen filters or traps. Finally, light weight contaminates, such as plastics, styrofoam, wood, adhesives and entrained air, can be the most difficult to remove. Various approaches to the removal of light weight contaminates have been proposed, including screens and skimmer devices.
Pulp fiber screening technology has practical limits defined by screen pore size and hydraulic pressure. As finer screens have been developed to filter unwanted contaminates, increased hydraulic horsepower has been required to drive the pulp therethrough. However, the high degree of screening currently required to produce acceptable quality paper results in energy inefficiencies. The removal of light weight contaminates, such as foldable bits of plastic sheeting, are especially problematic to remove by conventional screening techniques.
Prior art collection traps for light weight contaminates are also unsatisfactory. Most such traps provide an open collection area for buoyant light weight contaminates, which are then skimmed off the top. This skimming action agitates the rising light weight contaminates, and recirculates them into the pulp batch. Furthermore, this system requires an undesirable number of moving parts, which increases the likelihood of machine failure.
Traps for heavy contaminates in the prior art are also inadequate. Some models include a lower heavy contaminate collection pocket, which is periodically cleared by a grapple lowered from the top. Again, this requires unnecessary machinery and produces circulatory agitation, which prevents both light and heavy contaminates from efficiently separating.
Furthermore, such prior art devices do not permit a continuously adjustable range of decontamination depending upon the quality of the paper product desired. Prior art pulp decontaminators are also incapable of processing sufficiently large amounts of pulp to create an economy of scale.
Therefore, there exists in the art a long felt need for an improved pulp decontamination apparatus. Despite the apparent need for such pulp processing alternatives, there have been none which satisfactorily provide these desirable qualities. Accordingly, there is a need in the art for an improved apparatus and method for decontaminating pulp.